Fluid filters are commonly used in a variety of applications, including hydraulic systems, fuel systems and lubrication systems. Such filters generally include a filter element enclosed within a housing and mounted on a filter head. The filter head is usually incorporated into a fluid line of the slow system. Thus, the fluid head generally includes an inlet port, whereby fluid flow is received and directed into the filter or filter assembly. The filter head also generally includes outlet means by which fluid is received from the filter assembly, following filtration, and is directed back into a fluid flow-line.
Frequently used filter or filter assemblies are of the spin-on type, such as the one described in U.S. Pat. No. 4,369,113, incorporated herein by reference. The filter head assembly of the present invention is particularly adapted for use with such spin-on filters; however the principles may be employed with other types of filter systems.
Generally, such filter assemblies provide for the removal of undesired particles from a fluid line. Eventually, the filter elements of such assemblies may become clogged, prohibiting substantial fluid flow across the filter element. When such condition occurs, pressure on the upstream side of the filter assembly, relative to the downstream side, may become substantial. Also, the volume of fluid flow from the outlet end would become reduced and quite possibly could be entirely stopped.
The above type of blockages in fluid flow lines can pose numerous problems. For example, should fluid flow outward from the filter head at an appropriate rate substantially stop, then machinery located downstream may become damaged. Further, the increased pressure on the upstream side of the filter may result in rupturing of fluid seals, or damage to machinery located upstream of the filter. Also, should the upstream pressure become great enough, the filter itself may rupture or collapse, possibly resulting in a release of undesired matter from the filter, which can damage downstream equipment or occlude fluid lines.
To alleviate some of the above-described problems, a filter system may include a bypass line, operated by means of a relief valve, to permit fluid flow to selectively circumvent the filter in response to substantial occluding or plugging of the filter assembly. While numerous arrangements are possible, generally such bypass lines are of two basic types. In the first, when substantial plugging of the filter occurs, the relief valve permits fluid flow to merely circumvent the filter, and lead back into the main fluid line. For this type of arrangement, the fluid flowing into the downstream machinery will not have been filtered; however, at least downstream machinery will be protected from loss of substantial fluid pressure.
For the other type of arrangement, generally the relief valve operates to permit fluid flow into a line which is directed back to a fluid reservoir or elsewhere. While downstream equipment may not be protected under such circumstances, at least the filter assembly and any upstream equipment are protected from substantial increases in pressure. Also, such an arrangement may be useful when downstream machinery can tolerate a reduction in fluid flow, but not unfiltered fluid.
Conventional relief valves may be of numerous types. For example, a differential valve may be used to sense the pressure differential between the upstream and downstream sides of the filter. Should the pressure of the upstream side relative to the downstream side become sufficiently great, such a valve would open, permitting a circumventing flow of either of the two types described above. This type of valve generally includes a valve member therein which receives upstream and downstream pressure against opposite ends or sides thereof. Should the pressure of the upstream side increase relative to the downstream side, such a valve member will move within the valve body, generally opening a flow passageway for fluid to escape through an auxiliary or outlet line.
Generally, for conventional arrangements, the valve body defines a longitudinal chamber in which the piston member is slidably retained. The longitudinal chamber has a first end in communication with an upstream side of the filter assembly, and a second end in communication with the downstream side of the filter assembly. The valve member, again, is positioned between the two inlet ends of the valve chamber, and is slidable therebetween.
Also, such valve assemblies generally include a seal means providing selected sealing or seating of the piston valve member against the valve body in a manner permitting the inlet end of the valve body to be substantially sealed until pressure relief is intended. Further, such valve bodies generally include a lateral outlet aperture or takeoff aperture positioned substantially laterally with respect to the longitudinal axis of the valve body, permitting fluid flow therethrough when the relief valve is opened. As the piston member moves away from the first inlet, fluid flow through the valve body and out the lateral takeoff aperture is permitted. The fluid flow takeoff aperture is in communication with either the fluid line downstream of the filter assembly or with the fluid reservoir, depending upon which of the previously described systems is used.
The lateral takeoff aperture generally provides a lateral low-pressure area within the valve body. As will be seen from the detailed description, for conventional systems this may result in a lateral pressure differential against a side of the valve member and within the valve body. Should this occur, the valve member may tend to be pressed against a side of the longitudinal chamber, increasing friction and wear and generally disrupting smooth movement of the valve member and proper operation of the relief valve. This can become a particular problem when very high sensitivity to pressure differentials across a filter is desired; or, when very quick, smooth, operation of the relief valve is needed.
As indicated previously, generally the filter assembly is attached to a filter head by conventional means such as those described in U.S. Pat. No. 4,369,113. Such filter heads are preferably die-cast as a single unit, with appropriate lateral bores or holes drilled therein following the casting, to provide for attachment to a fluid line and to filter means. It would be preferred that a relief valve body be capable of being cast directly into the filter head at the time of the filter head assembly; for convenience, for reduction of expense; and for efficiency of operation without substantiated risk of leakage. However, previous filter heads have not generally provided for this, especially in arrangements wherein the valve body has means correcting for the problems described above.
The second type of relief valve generally operates more directly in response to absolute upstream fluid pressures, rather than in response to a differential between substantial upstream and downstream pressures. Such a valve generally includes an inlet and an outlet, the inlet being blocked by a valve member biased against the inlet, in sealing engagement, until an appropriate and selected upstream pressure is reached. When the pressure limit is reached, the valve member is pushed out of sealing engagement with the inlet aperture, permitting fluid flow into the valve and therethrough by means of the outlet. Generally, a spring or the like provides biasing of the valve member against the inlet aperture, until the selected pressure limit is reached.
It would also be preferred that this latter type of relief valve assembly be such as to be capable of formation by die-casting into a filter head of a typical assembly; again to facilitate manufacture and use without substantial leakage. It would be further preferred that such a type of relief valve be capable of formation in a system which may alternatively be easily used to form the first type of valve described above, at least with only relatively minor modifications. In this manner, considerable ease of manufacture of either type might be achieved at reduced cost.
Generally, what has been needed has been a relief valve assembly and filter head assembly appropriate for utilization in the modes previously described, and including means therein reducing problems from lateral fluid pressures operating against a sliding valve member. As will be seen, the instant invention includes such means, and other advantageous improvements.